Systems and methods for determining device temperature

ABSTRACT

Circuitry for measuring and/or monitoring device temperature may include a first node coupled to ground, and a second node and a first resistor coupled in series to ground and in parallel to the first node. A first current driven to the first node and a second current driven to the second node can be selected such that a first voltage measured at the first node and a second voltage measured at the second node are substantially equal. The circuitry may also include a third node and a second resistor coupled in series to ground. A third current driven to the third node can be selected such that a third voltage measured at the third node is substantially equal to a reference voltage. Measures of the second and third currents and measures of the first and second resistors can be used to determine device temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to the operation ofsemiconductor devices.

2. Related Art

A thermometer onboard a device such as an integrated circuit (e.g., aprocessor or microprocessor) can be used to measure the operatingtemperature of the integrated circuit. Operation of the device can thenbe managed according to how the operating temperature compares to thedesign limit temperature. If, for example, the operating temperature ofa microprocessor is less than its design limit, the frequency at whichthe microprocessor is operating can be increased, allowing themicroprocessor to perform tasks more rapidly. Conversely, if amicroprocessor is operating at a temperature exceeding the design limit,its frequency can be reduced to extend the life of the microprocessor.

Accurate measurements of temperature can be important to help ensurethat an integrated circuit does not exceed its design limit, especiallyif operation at or near the design limit is anticipated for any lengthof time.

SUMMARY OF THE INVENTION

Embodiments in accordance with the present invention provide methods andsystems for accurately measuring temperature in, for example, a devicesuch as an integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the present invention and,together with the description, serve to explain the principles of theinvention. The drawings referred to in this description should not beunderstood as being drawn to scale except if specifically noted.

FIG. 1 is a diagram of a system for measuring temperature according toone embodiment of the present invention.

FIG. 2 is a diagram of a system for measuring temperature according to asecond embodiment of the present invention.

FIG. 3 is a flowchart of a method for measuring temperature inaccordance with one embodiment of the present invention.

FIG. 4 is a flowchart of a method for monitoring temperature inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the various embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

While the invention will be described in conjunction with theseembodiments, it will be understood that they are not intended to limitthe invention to these embodiments. On the contrary, the invention isintended to cover alternatives, modifications and equivalents, which maybe included within the spirit and scope of the invention as defined bythe appended claims. Furthermore, in the following detailed descriptionof the present invention, numerous specific details are set forth inorder to provide a thorough understanding of the present invention.However, it will be recognized by one of ordinary skill in the art thatthe present invention may be practiced without these specific details.In other instances, well-known methods, procedures, components, andcircuits have not been described in detail as not to unnecessarilyobscure aspects of the present invention.

Some portions of the detailed descriptions that follow are presented interms of procedures, logic blocks, processing, and other symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the means used by thoseskilled in the data processing arts to most effectively convey thesubstance of their work to others skilled in the art. A procedure, logicblock, process, etc., is here, and generally, conceived to be aself-consistent sequence of steps or instructions leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated in a computersystem. It has proven convenient at times, principally for reasons ofcommon usage, to refer to these signals as bits, bytes, values,elements, symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present invention,discussions utilizing terms such as “determining” or the like, refer tothe action and processes (e.g., flowcharts 300 and 400 of FIGS. 3 and 4,respectively) of a computer system or similar intelligent electroniccomputing device (generally, a controller), that manipulates andtransforms data represented as physical (electronic) quantities withinthe computer system's registers and memories into other data similarlyrepresented as physical quantities within the computer system memoriesor registers or other such information storage, transmission or displaydevices.

FIG. 1 is a diagram of a system 100 for measuring and/or monitoringtemperature according to one embodiment of the present invention. FIG. 2is a diagram of a system 200 for measuring temperature according to asecond embodiment of the present invention. In general, the elements ofFIGS. 1 and 2 are described according to the functions they perform.However, elements may perform functions in addition to those describedherein. Also, functions described as being performed by multipleelements may instead be performed by a single element. Similarly,multiple functions described as being performed by a single (e.g.,multifunctional) element may instead be divided in some way amongst anumber of individual elements. Furthermore, the systems of FIGS. 1 and 2and each of their elements may include elements other than those shownor described herein.

In the example of FIG. 1, system 100 includes first circuitry 102 andsecond circuitry 104. In one embodiment, first circuitry 102 includes avariable first current source I1, a variable second current source I2, afirst p-n junction Q1 (e.g., a diode), a second p-n junction Q2 (e.g., adiode), and a first resistor R1, while second circuitry 104 includes avariable third current source I3 and a second resistor R2. In oneembodiment, system 100 also includes a comparator 112 and a controller114.

An important point is that, in one embodiment, a large number ofcurrent-source elements, laid out physically together in an array, areused to construct the three current sources I1, I2 and I3. In such anembodiment, all of the current-source elements are “identical” (that is,virtually identical), consistently driving identical small currents. Inone such embodiment, each element is adjustable in an analog fashion byone or more analog control input pins or other means that can receive ananalog control to adjust the current. For example, each current-sourceelement can be a single PMOS transistor (operated in the saturationregion, as is well known). The analog control pin for each such elementcan be the gate pin of the PMOS transistor. In a more complex design,each current-source element can be comprised of a current-source PMOS, acascode PMOS and one or two transistors for disabling the element. Thislatter type of element would perform better than the former but uses twoanalog control input pins: one for the current-source PMOS gate and onefor the cascode PMOS gate. In one embodiment, the voltage on the analogcontrol pin(s) of all current-source elements is the same. This can bedone by tying all of the analog control input pins together. (In thecase of the more complex element just described, all the current-sourcePMOS gates are commoned and all the cascode PMOS gates are commoned.) Inanother embodiment, these analog control pins are accessed throughanalog gates controlled by logic circuitry that either apply the analogcontrol voltage to each current-source element, or apply a disabling(high) voltage to deselect certain current-source elements. In thisfashion, all selected elements will drive out identical currents whileall deselected elements will drive out zero current. In any case, eachselected current-source element will drive out the same current as everyother selected current-source element. The analog control voltage can besupplied by analog circuit action as shown in FIG. 2, where a servo loopor other device adjusts the current of all (activated) current-sourceelements in concert.

The servo loop or other device adjusts the current of all (activated)current-source elements in concert so that the current driven by thecurrent-source elements varies with temperature and, in fact, isproportional to absolute temperature. A portion of a system that canperform such a function is that shown as 102 in FIG. 1 and is describedin more detail below. In FIG. 2, the circuitry block 202 performs thisfunction. To reiterate, an important point of the thermometer designdescribed herein is that all of the current-source elements arecontrolled in concert to have (virtually) identical currents that areproportional to absolute temperature.

As mentioned, each of the three current sources I1, I2 and I3 may becomposed of a number of these current-source elements. This isaccomplished by wiring together all the output pins of allcurrent-source elements that comprise the current source I1, wiringtogether all the output pins of all current-source elements thatcomprise the current source I2, and wiring together all the output pinsof all current-source elements that comprise the current source I3. Evendisabled current-source elements can have the output pin connected, butwill contribute no current. The number of elements that make up I1 andI2 may be the same or different, depending on the design details, andmay be programmable or not. The elements that make up I3 areprogrammable by a logic control device that can select (activate) thedesired number of current-source elements. In this fashion, the currentsource I1 can be made up of a number of identical current-sourceelements, say κM (an integer), where κ is a rational number and M is aninteger determined by details of the system design. For example, M canbe 8 and κM can be 16, in which case κ is 2. As another example, M canbe 17 and κM can be 23 current-source elements, in which case κ is23/17. Thus, the current i1 driven by the current source I1 is thenumber κM multiplied by the current from a single current-sourceelement. Similarly, the current source I2 can be made up of a number ofidentical current-source elements, say M. Thus, the ratio i1/i2 of thecurrent driven by the current source I1 divided by the current driven bythe current source I2 is κ. This ratio can be made quite precise, evenaccurate to three significant figures in a practical circuit. Supposethat the number of current-source elements in the current source I3 isN. Then the ratio i3/i2 of i3, the current driven by the current sourceI3 divided by i2, is N/M to high precision. Such precision is used toprovide an accurate thermometer system as described herein. In this way,the current-source elements all drive the same current while the currentsources I1, I2 and I3 each drive a respective different current by beingcomprised of different numbers of identical such current-sourceelements. Because at least one current source, I3, has a programmablenumber, the integer N should also be programmable.

Out of the large array of current-source elements, the choice of whichcurrent-source elements to wire together to make up each of the currentsources I1, I2 and I3 is made in such a way as to improve the accuracyof the ratios between the three sources. This may be done throughcentroiding the current-source elements, as is well understood by thoseskilled in the art. The current-source elements chosen to be wiredtogether to make up the current source I1 can be physically positionedwithin the array in a symmetrical pattern around a “centroid” point inthe array, typically a point in the center of the array. Similarly,those current-source elements chosen to be wired together to make up thecurrent source I2 can be physically positioned within the array in asymmetrical pattern around the same centroid point in the array. Thosecurrent-source elements chosen to be wired together to make up thecurrent source I3 can also be centroided about the same point in a waythat they remain centroided as the number N of activated current-sourceelements is programmed to different numbers.

In one embodiment, first circuitry 102 is a portion of a typical bandgap(e.g., silicon bandgap) reference circuit. In general, first circuitry102 is a precision circuit that supplies a voltage Vout that issubstantially insensitive to the circuitry's supply voltage andoperating temperature. The voltage Vout may be a full or fractionalbandgap voltage, depending on the type of circuit, and is accuratelyknown. Only certain elements of a bandgap reference circuit are shownand described herein. More specifically, in the embodiment of FIG. 1,the elements of a bandgap reference circuit that are relevant to anunderstanding of the present embodiment are illustrated while otherelements not relevant to that understanding are left out.

In the example of FIG. 1, p-n junction Q1 has an anode coupled to node 1and a cathode coupled to ground. The voltage at node 1 relative toground is termed “VBE1” (voltage between base and emitter). The p-njunction Q2 has an anode coupled to node 2 and a cathode coupled toground. The voltage at node 2 relative to ground is termed “VBE2.” Sincethe cathodes of both diodes Q1 and Q2 are commoned, the relative voltagebetween node 1 and node 2, referred to herein as “ΔVBE,” is thedifference between the two base-emitter voltages. This difference willarise by making sure that the current density in Q2 is lower than thatin Q1. A first resistor R1 is coupled between node 2 and node 3. Thevoltage across R1 is termed “VR1.”

In the example of FIG. 1, the p-n junctions Q1 and Q2 may be differentsizes and Q2 may be larger than Q1. The junction area of Q2 is anaccurately known multiple “α” of the junction area of Q1: Q2=α·Q1.Theoretically, a may or may not be greater than 1, though in practice itis generally chosen in the design to be greater than 1, perhaps between5 and 40. Further, α may or may not be an integer and quite commonly isnot. In one embodiment, the p-n junctions Q1 and Q2 are implemented asan array of well-matched (e.g., virtually identical), co-locatedelements that are wired together and commonly centroided—that is, theelements of each diode are symmetrically located about a common physicalpoint in the center, or at about the center, of the array. (It isunderstood that elements may not be perfectly identical due tomanufacturing variability and tolerances.) Q1 may consist of K elementsand Q2 may consist of αK elements, and as such the ratio α between thejunction areas Q2 and Q1 can be accurately determined. In this example,K and αK are integers.

In the example of FIG. 1, current sources I1 and I2 are variable(adjustable) current sources. That is, the amount of current may beadjusted in a linear or analog fashion by a control, such as the signalICtl. Current source I1 drives a current i1 into the anode of Q1 at node1, and current source I2 drives a current i2 into R1 and Q2 at node 3.The currents i1 and i2 may be of different magnitudes and i1 may begreater than i2. The current i1 is an accurately known multiple “κ” ofthe current i2: i1=κ·i2. In one embodiment, this is accomplished using acurrent mirror scheme. In another embodiment, ICtl may be supplied by afeedback circuit as illustrated in FIG. 2. In this fashion, the currentdensity in Q1 is ακ times that in Q2, with ακ greater than one. In oneembodiment, the current sources I1 and I2 are implemented as an array ofwell-matched (e.g., virtually identical), co-located current-sourceelements that are wired together and commonly centroided. In one suchembodiment, I2 consists of M current-source elements and I1 consists ofκM current-source elements, and as such the ratio κ between the currentsi1 and i2 can be accurately determined. As will be seen, thecurrent-source elements that comprise I1 and I2 are adjusted in analogfashion in concert, such that the ratio κ between the currents i1 and i2is maintained.

Current source I3 is also a variable current source which supplies acurrent i3. In one embodiment, current source I3 includes a number N ofwell-matched, co-located and centroided current-source elements. Thesecurrent-source elements may also be virtually identical with those thatcomprise I1 and I2 and may be commonly centroided in the array with thecurrent-source elements that comprise I1 and I2. As such, the ratio N/Mbetween the currents i3 and i2 can be accurately determined. Thecurrent-source elements that comprise I3 are adjusted in analog fashionin concert with the current-source elements that comprise I1 and I2,such that the ratio N/M between the currents i3 and i2 is maintained.

Further, in one embodiment, current source I3 is also a digitallyprogrammable current source that is controlled using a digital signal N.In one such embodiment, the amount of current i3 that is supplied bycurrent source I3 is a function of the number of current-source elementsthat are turned on (activated) by a digital signal N. In general,current source I3 is a variable current source that supplies an amountof current that is proportional to the value of a digital input signalN.

In one embodiment, the digital input signal N is an eight-bit (b₇, b₆, .. . , b₀) digital signal, with each bit turning on (or off) some numberof current-source elements. For example, the most significant bit (b₇)can control (turn on or off) 128 (=2⁷) current-source elements, thesecond most significant bit (b₆) can control 64 (=2⁶) current-sourceelements, the third most significant bit (b₅) can control 32 (=2⁵)current-source elements, and so on, with the least significant bit (b₀)controlling 1 (=2⁰) current-source element. In one embodiment, thecurrent-source elements that may be switched on at a particular time areselected in centroidal (or symmetrical) fashion. Under control of aneight-bit signal, current source I3 can provide up to 256 levels ofcurrent. At the same time, the current from each of the current-sourceelements that comprise I3 are adjusted in an analog fashion in concertwith those current-source elements that comprise I1 and I2. It isimportant that the current from each of the current-source elements thatcomprise I3 is not affected by the number N of elements that are turnedon by the digital signal N. It should be understood that, as the valueof N is programmed, there will be some number of current-source elementsthat are turned on to contribute to the current i3 or turned off so thatthey contribute no current to i3. The number that is turned on by thedigital signal N will be equal to N.

It may be desirable to have some number of current-source elementsalways turned on, in addition to the number N, and always contributingto the current i3. This can be accomplished using, for example, anine-bit signal, in which one bit (e.g., the most significant bit) isset such that some current-source elements are always turned on, withthe remaining eight bits used to control other current-source elementswith up to 256 levels of current. The use of nine bits in this manneralso increases the possible range of N, from 0-255 to 256-511, forexample. Larger values of N reduce the associated quantization error,increasing the accuracy at which the temperature T can be determined.Having a number of current-source elements always on, in addition to the255 that are controlled by the 8-bit digital signal N, also can shiftthe operational temperature range of the circuit to a more desirableregion of absolute temperature.

Current source I3 drives a current i3 into R2 at node 4. As mentionedabove, the current sources I1, I2 and I3 are adjusted in concert in ananalog fashion. Further, current source I3 is also separatelyadjustable; that is, current source I3 can be adjusted independentlyfrom current sources I1 and I2. While the current source I3 is adjustedindependently of the current sources I1 and I2, the ratio of i3 to i2(or i3 to i1) can be accurately determined. In one embodiment, theelements of current source I3 and the elements of current sources I1 andI2 are commonly centroided. As such, the ratio of i2/i3 is accuratelyrepresented as the ratio M/N.

The voltage across R2 is termed “VR2.” The resistors R1 and R2 havedifferent resistances r1 and r2, respectively, and the ratio P betweenthe resistance values of R1 and R2 is accurately known (P=r2/r1). Theresistors R1 and R2 can each be realized using an array of virtuallyidentical, co-located resistors that are wired together and commonlycentroided, in which case the ratio P between the resistances of R2 andR1 can be accurately determined.

In one embodiment, comparator 112 (e.g., a differential comparator) isconnected to the current source I3 and to the first circuitry 102. Morespecifically, in such an embodiment, one input of comparator 112 isconnected to node 4 between the current source I3 and resistor R2, andthe other input of comparator 112 is connected to Vout, which is anaccurately known voltage, relative to system ground, and which istemperature-independent.

In one embodiment, system 100 also includes a controller 114 thatsupplies the aforementioned digital input signal N to current source I3and that is also coupled to the output of comparator 112.

System 100 can be incorporated into an integrated circuit or some othertype of semiconductor device in order to determine a temperature T forthat circuit/device. More specifically, the temperature is determined atQ1 and Q2, which are co-located. The temperature at Q1 and thetemperature at Q2 are considered to be equal and representative of thetemperature of the circuit or device incorporating the system 100.

As described above, Q1 and Q2 comprise a pair of p-n junctions that havean accurately known ratio of current density, κα, and have substantiallythe same junction temperature at all times. By design, the currentdensity in Q1 will be higher and equal to κα times the current densityin Q2 and as such, the junction voltage of Q1 will be greater than thatof Q2. For such a pair of p-n junctions, ΔVBE, the difference betweenthe junction voltages, will obey the following well-known relationshipwhich can be applied to obtain an absolute temperature T:

ΔVBE=n(k/q)(T)In(γ);   (1)

where “n” is the ideality factor of a p-n junction, “k” is the Boltzmannconstant, “q” is the electron charge, “T” is absolute temperature, and“γ” is the ratio of the current density in Q1 to the current density inQ2 (γ=κα). In one embodiment, a value of n=1.008 is used. As statedpreviously herein, the relative voltage between node 1 and node 2 isequal to ΔVBE.

The temperature T can be determined using relationship (1) and system100 as follows. The currents i1 and i2 are adjusted in concert in alinear or analog fashion while maintaining the ratio κ. An analog signalsuch as ICtl can be used to make this adjustment. Additionally, ifdesired, a digital signal can be used to turn on some number M (and κM)of the current elements that constitute current sources I1 and I2, in amanner similar to that described above for current source I3.

In the example of FIG. 1, at initial power-up and subsequently astemperature changes, the currents i1 and i2 are adjusted in concert(along with the current-source elements in I3) by ICtl in a linearfashion until the voltage relative to ground at node 3 is made equal (orsubstantially equal) to the voltage relative to ground at node 1 (VBE1).An op-amp can be used to identify when this condition occurs (see FIG.2, below). When the voltage relative to ground at node 3 is equal to thevoltage relative to ground (VBE1) at node 1, the voltage across resistorR1 (VR1) will be equal to ΔVBE, the difference between VBE1 and thevoltage relative to ground at node 2 (VBE2). Thus, with this adjustmentat any given temperature, the voltage across resistor R1 (VR1) will beproportional to absolute temperature, in accordance with the relation(1) above.

By changing the value of the digital signal N, the current i3 is alsoadjusted until the voltage across resistor R2 (VR2) is equal (orsubstantially equal) to Vout. Because VR2=i3*r2 and ΔVBE=VR1=i2*r1, thenVout=i3*r2=i2*(i3/i2)*r1*(r2/r1)=(i3/i2)(r2/r1)*VR1. Thus,

T=Vout*(i2/i3)(r1/r2)*(q/(nk·In(γ)).   (2)

Once values for Vout, R1 and R2 are selected as a matter of designchoice, the quantity Vout*(r1/r2)*(q/(nk·In(γ)) is a known constant “β.”Thus,

T=β(i2/i3).   (3)

As mentioned above, in one embodiment, i2/i3=M/N. Thus,

T=β′/N,   (4)

where β′=β·M, and where N is the value of the digital signal when thecomparator 112 changes state. Note that, in an ideal sense, i3 is to berestored always to the fixed value Vout/R2. As temperature varies, ICtlwill readjust i1 and i2 in concert (along with the current-sourceelements in I3) to maintain the voltages at nodes 1 and 3 to be equal.Thus i3 departs from the “correct” value of Vout/R2. The controller 114digitally readjusts i3 to be equal once again to Vout/R2 through the useof N and the comparator 112. The value of N that was used to achievethis is then entered into the relation (4) to find the temperature.

Controller 114 has knowledge of the value of N and can applyrelationship (4) to calculate and output a value of the temperature T.In one embodiment, the midpoint of the interval in which the comparator112 changes state is used in relationship (4). For example, ifcomparator 112 changes state when N changes from 178 to 179 (actually,the digital signal equivalents of 178 and 179), then a value of Nequivalent to 178.5 can be used.

Systems 100 can be referred to as “quasi-static.” That is, thetemperature of the device is expected to change slowly enough relativeto the circuits' response time to be considered constant over the periodof time it takes to measure temperature. The first circuitry 102 settlesto a value of ICtl such that the voltage at node 3 equals the voltage atnode 1, while the temperature is unchanging. Controller 114 can thenfind a correct value of N, again before the temperature changessignificantly.

Therefore, by matching at accurate ratios (but not necessarily equating)I3 and R2 (and i3 and r2) to certain elements and attributes of abandgap reference circuit (specifically, I2 and R1, and i2 and r1), theoperating temperature of a device can be readily and accuratelydetermined, without having to introduce substantial additionalcircuitry. For example, a separate servo-loop is not needed to controlthe amount of current supplied by current source I3. Another advantageof system 100 is that the value of N is readily determined and is knownto a high degree of granularity (for example, there can be 256 levels ofgranularity), which means that temperature can also be determined to ahigh degree of granularity. Furthermore, it is not necessary to measurethe currents supplied by current sources I1, I2 and I3, because it isonly necessary to know the ratio between i2 and i3.

In the example of FIG. 1, a known reference voltage Vout is supplied bya bandgap reference circuit (first circuitry 102). Certain elements ofsecond circuitry 104 are accurately matched to elements internal to thatbandgap reference circuit 102. In general, any voltage that isaccurately known, from a “closed” bandgap reference circuit or otheraccurately known temperature-independent source, can be used as Vout,with the condition that the known reference voltage is relative to thesame reference or ground as VR2. In that case, an additional circuitryis needed. Such a system is shown in FIG. 2.

FIG. 2 is a diagram of a system 200 for measuring temperature accordingto a second embodiment of the present invention. While system 100 ofFIG. 1 represents a relatively specific implementation of a devicethermometer, system 200 represents a broader, more generalimplementation.

In the example of FIG. 2, system 200 includes first circuitry 202 andsecond circuitry 204. In one embodiment, first circuitry 202 includes avariable first current source I1, a variable second current source I2, afirst p-n junction Q1, a second p-n junction Q2, a first resistor R1,and an op-amp 216, while second circuitry 204 includes a variable thirdcurrent source I3 and a second resistor R2. In one embodiment, system200 also includes a comparator 112 and a controller 114.

System 200 is used to determine a temperature T in a manner similar tothat described above. For the current source I2, the number of matchedcurrent-source elements may be fixed at M. The number of matchedcurrent-source elements for I1 might then be fixed at KM. Accordingly,the currents of I1 and I2 have the ratio κ.

Also, Q1 and Q2 might be made up of K and αK bipolar elements,respectively, and are centroided, so that the emitter-base junctionareas have the ratio α. Thus, the current densities between theemitter-base junctions of Q1 and Q2 have the ratio γ, wherein γ=κα, andκα must be greater than 1.

When ICtl is adjusted, the voltages at node 1 and at node 3 will crossat some point, which is identified using op-amp 216. At that point,VR1=ΔVBE, which is equal to a known constant (n(k/q)(T)In(γ)) times theabsolute temperature (see the discussion of relationships (1) and (2)above). As device temperature changes, in the example shown in FIG. 2,the op-amp will adjust (servo) ICtl to keep the voltage at node 1 equalto the voltage at node 3.

Like system 100, system 200 can be referred to as quasi-static. Thecircuitry performs fast enough and the temperature changes slowly enoughso that, effectively, the voltage at node 1 is always equal to thevoltage at node 3, and hence VR1 is always proportional to absolutetemperature.

The current sources I2 and I3 also match because, for example, I3 alsomay be comprised of current-source elements with layouts identical tothose of I2. Consequently, as controller 114 adjusts N to make VR2 matchVknown, the current ratio i3/i2 will be equal to N/M.

The resistors R1 and R2 are matched and centroided and their respectiveresistances have the ratio P (P=r2/r1). Accordingly, the voltage acrossR2 (VR2) is equal to (NP/M)*VR1. The temperature T can be calculatedusing relationships (2), (3) or (4) above. As described above, it is notnecessary to know the values of i1, i2 and i3, nor even the values of r1and r2 nor the sizes of Q1 and Q2, as long as the ratios α, κ (and henceγ) and P are known.

FIG. 3 is a flowchart 300 of a method for measuring temperature inaccordance with one embodiment of the present invention. FIG. 4 is aflowchart 400 of a method for monitoring temperature in accordance withone embodiment of the present invention. Although specific steps aredisclosed in the flowcharts, such steps are exemplary. That is,embodiments of the present invention are well-suited to performingvarious other steps or variations of the steps recited in theflowcharts. It is appreciated that the steps in the flowcharts may beperformed in an order different than presented, and that not all of thesteps in the flowcharts may be performed. Some or all of the processesand steps of the flowcharts can be realized, in one embodiment, as aseries of instructions that reside in hardware or software and areexecuted by controller 114 of FIGS. 1 and 2.

In block 302 of FIG. 3, with reference also to FIGS. 1 and 2, a firstcurrent (e.g., i1) that is driven to a first node (e.g., node 1) and asecond current (e.g., i2) that is driven to a second node (e.g., node 3)are adjusted in concert, until a first voltage (e.g., VBE1) measured atnode 1 and a second voltage measured at node 3 are substantially equal.

In block 304, a third current (e.g., i3) that is driven to a third node(e.g., node 4) is adjusted until a third voltage (e.g., VR2) measured atnode 4 is substantially equal to a reference fourth voltage (e.g., Voutor Vknown).

In block 306, measures of the second and third currents (specifically,the ratio of i2 to i3) when the third and fourth voltages aresubstantially equal (specifically, when VR2=Vout or Vknown), andmeasures of the first and second resistors (specifically, the ratio ofr1 to r2), are used to determine a temperature, using relationship (2)for example. In one embodiment, node 1 includes a first p-n junction(e.g., Q1) having a first junction area and node 3 includes a second p-njunction (e.g., Q2) having a second junction area, and the ratio abetween the first and second areas, and the ratio κ between i1 and i2,are also used in relationship (2) to determine the temperature (γ=κα).

In one embodiment, the second current i2 is produced by using a firstnumber (M) of current-source elements, and the third current i3 isproduced using a second number (N) of current-source elements. In suchan embodiment, the first and second numbers can be used in relationship(4) to determine the temperature.

Embodiments in accordance with the present invention can also be used tomonitor temperature and to provide an indication (e.g., a flag) when aparticular temperature is reached or a temperature threshold is crossed.In other words, as can be seen from relationships (2) and (3), thetemperature T corresponds to the ratio of the values of i2 and i3. Byrearranging relationship (3), the ratio of i2/i3 corresponding to atemperature threshold T-threshold can be defined:

i2/i3=(T-threshold)/β.   (5)

In one embodiment, to monitor temperature against a temperaturethreshold, the digital value of N would be held at a fixed valuecorresponding to the temperature T-threshold, in accordance withrelation N=M(T-threshold)/β. The current source I2 can be controlled inan analog fashion such that the magnitude of the current i2 causes afirst voltage (e.g., VBE1) measured at node 1 and a second voltagemeasured at node 3 to be substantially equal at all temperatures.Concurrently the current source I3 can be controlled such that themagnitude of the current i3 causes a third voltage (e.g., VR2) measuredat node 4 and a reference fourth voltage (e.g., Vout or Vknown) to besubstantially equal at T-threshold. In other words, ICtl (or M) and N,as well as the other design parameters associated with Q1, Q2, R1 andR2, are set at values that, if utilized in relationships (2), (3) or(4), would cause VR2 to rise to equal a reference fourth voltage (e.g.,Vout or Vknown) as the temperature rises to a value of T-threshold.

Thus, for example, the systems 100 and 200 of FIGS. 1 and 2 are inessence operated at a condition meant to detect when the devicetemperature (measured at Q1 and Q2) reaches T-threshold. As thetemperature at Q1 and Q2 increases, the circuit of block 102 of system100 or the circuit of block 202 of system 200 (FIG. 2) will increase thecurrent i2 to keep the voltages at nodes 1 and 3 equal. In concert, thecurrent i3 (at the fixed value of N) is increased and thus the VR2 willincrease. At T-threshold, VR2 will equal Vout or Vknown. When VR2 andVout or Vknown are equal, comparator 112 will notify controller 114,which in turn can provide an indication that the threshold temperaturehas been reached. Different values of N can be selected and utilized toidentify and implement different temperature thresholds.

FIG. 4 is a flowchart 400 of a method for monitoring temperature in adevice in accordance with one embodiment of the present invention. Inblock 402, with reference also to FIGS. 1 and 2, a first current (e.g.,i1) is driven to a first node (e.g., node 1) and a second current (e.g.,i2) is driven to a second node (e.g., node 3).

In block 404, a third current (e.g., i3) is driven to a third node(e.g., node 4). The magnitudes of the first, second and third currentsare selected such that when the temperature T of the device reaches aspecified threshold (e.g., T-threshold), while a first voltage measuredat node 1 (e.g., VBE1) and a second voltage measured at node 3 aremaintained to be substantially equal, a third voltage measured at node 4(e.g., VR2) and a reference fourth voltage (e.g., Vout or Vknown) willbe substantially equal.

In block 406, if the conditions mentioned in block 404 are satisfied,then an indication that the threshold temperature has been reached canbe provided.

In summary, embodiments in accordance with the present invention providemethods and systems for accurately measuring and monitoring temperaturein, for example, a device such as an integrated circuit. By matchingcertain elements and attributes of a first portion (e.g., firstcircuitry 102 or 202) of a thermometer system with elements andattributes of a second portion (e.g., second circuitry 104 or 204) ofthe thermometer system, the operating temperature of a device can bereadily and accurately determined. Furthermore, it is not necessary tomeasure the magnitudes of currents, resistances and junction areas inthe first and second portions of the system, as long the respectiveratios (e.g., κ, α and P) are known.

Embodiments in accordance with the present invention are thus described.While the present invention has been described in particularembodiments, it should be appreciated that the present invention shouldnot be construed as limited by such embodiments, but rather construedaccording to the below claims.

1. A system for determining temperature, said system comprising: firstcircuitry comprising: a first node coupled to ground; and a second nodeand a first resistor coupled in series to ground and in parallel to saidfirst node, wherein a first current driven to said first node and asecond current driven to said second node are selectable such that afirst voltage measured at said first node and a second voltage measuredat said second node are substantially equal; and second circuitrycoupled to said first circuitry and comprising a third node and a secondresistor coupled in series to ground, wherein a third current driven tosaid third node is selectable such that a third voltage measured at saidthird node is substantially equal to a reference fourth voltage, andwherein measures of said second and third currents and measures of saidfirst and second resistors are useful for determining said temperature.2. The system of claim 1 wherein said first circuitry comprises abandgap reference circuit that outputs said fourth voltage.
 3. Thesystem of claim 1 wherein said first node comprises a first p-n junctionhaving a first junction area and said second node comprises a second p-njunction having a second junction area that is different from said firstjunction area, wherein a ratio between measures of said first and secondareas is also useful for determining said temperature.
 4. The system ofclaim 1 wherein said first circuitry further comprises a first variablecurrent source for driving said first current and a second variablecurrent source for driving said second current.
 5. The system of claim 4wherein said first variable current source and said second variablecurrent source are adjustable in concert such that a ratio of measuresof said first and second currents remains substantially constant if saidfirst and second currents are changed, wherein said ratio is also usefulfor determining said temperature.
 6. The system of claim 4 wherein saidsecond circuitry further comprises a third variable current source thatis adjustable independently from said first and second variable currentsources.
 7. The system of claim 6 wherein said second variable currentsource and said third variable current-source each comprise a respectiveplurality of current-source elements, wherein a first number ofcurrent-source elements is used to drive said second current and asecond number of current-source elements is used to drive said thirdcurrent, and wherein further said first and second numbers are useful assaid measures of said second and third currents.
 8. The system of claim1 further comprising a comparator coupled to said third node and thatreceives said third voltage as one of its inputs and said fourth voltageas another one of its inputs, wherein an output of said comparatorchanges state if a measure of said third voltage crosses a thresholdestablished by a measure of said fourth voltage.
 9. The system of claim1 wherein said second circuitry further comprises: a variable currentsource comprising a plurality of current-source elements, wherein anumber of said current-source elements is selected to produce said thirdcurrent; a controller coupled to said variable current source, whereinsaid controller changes said number of current-source elements to changesaid third voltage; and a comparator coupled to said third node and thatreceives said third voltage as one of its inputs and said fourth voltageas another one of its inputs, wherein an output of said comparatorchanges state if a measure of said third voltage crosses a thresholdestablished by a measure of said fourth voltage, and wherein furthersaid controller records said number of current-source elements inresponse to said comparator changing state.
 10. The system of claim 1wherein said first circuitry further comprises an op-amp coupled to saidfirst and second nodes and operable for comparing said first and secondvoltages.
 11. A method of measuring temperature, said method comprising:adjusting a first current that is driven to a first node and a secondcurrent that is driven to a second node until a first voltage measuredat said first node and a second voltage measured at said second node aresubstantially equal, wherein said first node is coupled to ground andwherein said second node and a first resistor are coupled in series toground and in parallel to said first node; adjusting a third currentthat is driven to a third node until a third voltage measured at saidthird node is substantially equal to a reference fourth voltage, whereinsaid third node and a second resistor are coupled in series to groundand in parallel to said first node; and using measures of said secondand third currents when said third and fourth voltages are substantiallyequal and measures of said first and second resistors to determine saidtemperature.
 12. The method of claim 11 further comprising generatingsaid fourth voltage using a bandgap reference circuit.
 13. The method ofclaim 11 wherein said first node comprises a first p-n junction having afirst junction area and said second node comprises a second p-n junctionhaving a second junction area that is different from said first junctionarea, wherein said method further comprises using a ratio betweenmeasures of said first and second areas to determine said temperature.14. The method of claim 11 further comprising: adjusting said firstcurrent and said second current in concert such that a ratio of measuresof said first and second currents remains substantially constant as saidfirst and second currents are changed; and using said ratio to determinesaid temperature.
 15. The method of claim 11 further comprising: drivingsaid second current using a first number of a first plurality ofcurrent-source elements; driving said third current using a secondnumber of a second plurality of current-source elements; and using saidfirst and second numbers as said measures of said second and thirdcurrents to determine said temperature.
 16. A method of monitoringtemperature in a semiconductor device, said method comprising: driving afirst current to a first node and a second current to a second node,wherein said first node is coupled to ground and wherein said secondnode and a first resistor are coupled in series to ground and inparallel to said first node; driving a third current to a third node,wherein said third node and a second resistor are coupled in series toground and in parallel to said first node, and wherein further saidfirst, second and third currents are selected such that when atemperature of said device reaches a specified threshold, a firstvoltage measured at said first node and a second voltage measured atsaid second node will be substantially equal and a third voltagemeasured at said third node and a reference fourth voltage will besubstantially equal; and providing an indication that said temperaturehas reached said threshold.
 17. The method of claim 16 furthercomprising generating said fourth voltage using a bandgap referencecircuit.
 18. The method of claim 16 wherein said first node comprises afirst p-n junction having a first junction area and said second nodecomprises a second p-n junction having a second junction area that isdifferent from said first junction area, wherein said method furthercomprises using a ratio between measures of said first and second areasto determine said temperature.
 19. The method of claim 16 furthercomprising: adjusting said first current and said second current inconcert such that a ratio of measures of said first and second currentsremains substantially constant as said first and second currents arechanged; and using said ratio to determine said temperature.
 20. Themethod of claim 16 further comprising: driving said second current usinga first number of a first plurality of current-source elements; drivingsaid third current using a second number of a second plurality ofcurrent-source elements; and using said first and second numbers asmeasures of said second and third currents to determine saidtemperature.